One troublesome and persistent problem during laundering operations is the tendency of some colored fabrics to release dye into the laundering solution which dye is then transferred onto other fabrics.
Manufacturers use many types of dye to color fabrics. Common fabric dyes include direct dyes used primarily to color cotton and rayon, acid dyes used primarily on nylon, wool, and silk, disperse dyes used primarily on polyester, nylon, and Spandex, azo dyes used primarily on cotton, rayon, and silk, reactive dyes used primarily on cotton and rayon, and vat dyes used primarily on cotton. Direct, acid and disperse dyes are in general readily released into washing solution while azo and vat dyes are not. When properly applied, reactive dyes chemically bond to cellulose and therefore are not readily solubilized; however, if improperly applied, reactive dyes may also release into the wash solution. Cotton, nylon, rayon and Spandex fabrics have a strong propensity to pick up solubilized or suspended dyes from solution, while polyester fabrics pick up such dyes to a lesser extent.
In the laundry operation, especially the operation involving automatic washing machines, dye transfer occurs mainly during the wash cycle, and very seldom, if at all, during the rinse cycle. Dye transfer during the wash cycle is caused by higher water temperature, longer cycle time, and much higher surfactant concentration in the wash cycle, as compared to the less stringent conditions of the rinse cycle.
Thus, those skilled in the art have focused efforts to inhibit dye transfer by adding dye transfer inhibitors to detergent compositions. For example, European Patent Application 265,257, Clements et al., published Apr. 27, 1988, discloses detergent compositions which prevent dye transfer, containing a detergent active (mixtures of anionic and nonionic are preferred), a detergent builder, and a polyvinylpyrrolidone (PVP) mixture. German Pat. No. 3,519,012, Weber et al., published Nov. 27, 1986, teaches a detergent composition comprising nonionic surfactants, PVP components, water-soluble cationic components, and builders, to prevent dye transfer during the wash.
Dye transfer inhibitors (DTI), such as PVP, appear to solubilize into the wash water to scavenge the free dye molecules, thus suspending the dyes and preventing them from redepositing onto fabrics.
DTI may interact with some detergent actives. For example, detergent compositions containing PVP and anionic surfactants usually have decreased dye transfer inhibition performance compared to those detergents containing PVP and nonionic surfactants. It is believed that anionic surfactants interact with PVP in the wash cycle, and reduce PVP's ability to interact with free dye molecules.
All percentages, ratios, and parts herein are by weight unless otherwise stated.